EXACT BRAGG BACKSCATTERING OF X-RAYS

Exact 180 degrees Bragg scattering of pulsed synchrotron radiation was observed by using a semitransparent detector and a time-of-flight tec hnique. The angular dependences of Bragg scattering of monochromatic 1 4.413 keV x rays with only 0.5 mu eV bandwidth were studied by utilizi ng the (1 3 (4) over bar 28) reflection of an Al2O3 crystal at differe nt temperatures. By heating the crystal first the exact backscattering shows up achieving maximum intensity and 1.7 mrad angular width at 37 2.40 K. By increasing the temperature it develops into the usual Bragg reflection with much narrower angular profile. The measured dependenc es are in agreement with the theory. The fit is sensitive to a 5x10(-9 ) Angstrom variation of interplanar distance.